KR20170111746A - Electrode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides an electrode for a lithium secondary battery comprising an active material layer and a current collector, wherein the active material layer includes an active material and a hygroscopic material, and the hygroscopic material is disposed between the spaces formed by arranging the active material in the active material layer, The electrode for a lithium secondary battery according to the present invention is characterized in that a hygroscopic material is disposed between the pores formed by the active material in the active material layer and water present in the electrode and the electrolyte can be removed, The side reaction in the battery can be eliminated, and the performance of the battery can be improved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery including the electrode,

The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery including the electrode. More particularly, the present invention relates to an electrode for a lithium secondary battery including a mixed conductive material and having improved high-temperature storage performance and low-temperature output, and a lithium secondary battery including the same.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

Generally, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly composed of a cathode including a lithium transition metal oxide as an electrode active material, a cathode including a carbonaceous active material, and a separator. Such a lithium secondary battery has a non-aqueous composition, and the electrode is generally manufactured by coating an electrode slurry on a metal foil. The electrode slurry includes an electrode active material for storing energy, a conductive material for imparting electrical conductivity, A binder for bonding the electrode foil to the electrode foil and a binder for providing a bonding force to each other, and a solvent such as N-methyl pyrrolidone (NMP). As the cathode active material, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide and the like are mainly used, and carbon materials are mainly used as the anode active material.

The positive electrode material mixture and the negative electrode material mixture are generally added with a conductive material for the purpose of improving the electrical conductivity of the active material. Particularly, since the lithium transition metal oxide used as the cathode active material has low electric conductivity, a conductive material is essentially added to the cathode mixture.

As the conductive material, for example, carbon materials such as graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black are mainly used. Or a particle shape and is positioned between the surface of the positive electrode active material and the gap formed between the positive electrode active materials to compensate for the low electrical conductivity of the positive electrode active material. On the other hand, the conductive material located on the surface of the positive electrode active material The pores on the surface of the positive electrode active material are blocked or the pores formed between the positive electrode active materials are blocked by the conductive material to thereby interfere with the movement of lithium ions or the diffusion of the electrolyte, .

In addition, when the battery is placed at a high temperature, the conductive material may cause a side reaction with the electrolyte, and the resistance of the electrode is increased due to the side reaction and the disconnection of the electrical network.

Therefore, it is required to develop a new technology that can solve the problems of the conventional conductive material as described above.

A problem to be solved by the present invention is to prevent the pore between the active material and the active material from blocking the pore between the active material, thereby reducing the resistance of the electrode, thereby improving the performance of the battery and suppressing side reactions with the electrolyte, To provide an electrode for a lithium secondary battery.

Another object of the present invention is to provide a lithium secondary battery including the electrode for the lithium secondary battery.

Another object of the present invention is to provide a method for manufacturing the electrode for a lithium secondary battery.

In order to solve the above problems,

An electrode for a lithium secondary battery comprising an active material and a conductive material,

Wherein the conductive material is a mixture of a point conductive material and a linear conductive material,

Wherein the conductive material has a surface area of 0.01 to 3 m ² per 1 g of the active material.

Further, in order to solve the above-mentioned other problems,

The present invention also provides a lithium secondary battery including the electrode for the lithium secondary battery.

Further, in order to solve the above-described problems,

(1) preparing a linear conductive material mixture comprising a binder and a linear conductive material;

(2) adding an electrode active material to the linear conductive material mixture and mixing to prepare a mixture; And

(3) preparing a slurry for an electrode active material by adding a point conductive material to a mixture of the linear conductive material mixture and the electrode active material and mixing them.

The electrode for a lithium secondary battery according to the present invention includes both a linear conductive material and a point conductive material so as to prevent the void conductive material from blocking the gap between the surface of the active material and the active material so that the lithium secondary battery exhibits excellent output, A side reaction with the electrolyte is reduced, and a lithium secondary battery having improved high-temperature storage characteristics can be provided.

1 is a graph showing the results of evaluation of a reference performance test (RPT) of each of the lithium secondary batteries manufactured in Example 2 and Comparative Examples 2 and 3. FIG.
FIG. 2 is a graph showing the results of measurement of the capacity retention ratio and resistance of each of the lithium secondary batteries manufactured in Example 2 and Comparative Examples 2 and 3. FIG.
3 is a graph showing the results of evaluating low-temperature output characteristics of each of the lithium secondary batteries manufactured in Example 2 and Comparative Examples 2 and 3. Fig.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The electrode for a lithium secondary battery according to the present invention comprises an active material and a conductive material, wherein the conductive material is a mixture of a point conductive material and a linear conductive material, and the conductive material has a surface area of 0.01 to 3.5 m ² per 1 g of the active material .

In general, the conductive materials may easily aggregate due to their hydrophobic properties. When only the conductive material is used as the conductive material according to such characteristics, the conductive material may aggregate to form voids formed between the active materials Which may cause a phenomenon that the air gap is closed. If the void-type conductive material blocks the pores between the active materials, it may interfere with the diffusion of the electrolyte in the electrode, thereby increasing the resistance of the electrode.

In addition, the point-like conductive material blocks the pores formed on the surface of the active material, thereby preventing the electrolyte from penetrating into the active material or penetrating lithium ions into the active material, thereby increasing the resistance of the electrode .

Therefore, since the electrode for a lithium secondary battery according to the present invention includes a mixture of the point conductive material and the linear conductive material as the conductive material, the linear conductive material is located on the surface of the active material or in the gap formed between the active materials, But rather exists in a form crossing between the active materials so that the point conductive material blocks the pores of the surface of the active material or accumulates on the pores formed between the active materials .

In addition, since the linear conductive material is present across the various active materials to increase the electrical contact between the active materials, when the conductive material undergoes a side reaction with the electrolyte at a high temperature, The phenomenon that the network is cut off can be minimized, and the increase in the resistance of the electrode can be suppressed as the electrical network is disconnected.

However, since the preceding conductive material has a higher specific surface area as compared with the point conductive material, there is a high possibility that the lithium ion battery may cause a side reaction due to the electrolyte during storage at a high temperature. Therefore, It is necessary to prevent side reactions caused by the electrolytic solution while solving the problem.

In the present specification, the conductive material has a surface area of 0.01 to 3.5 m ² per 1 g of the active material. When a certain amount of the active material and the conductive material is taken in the electrode for a lithium secondary battery, Surface area is from 0.01 to 3.5 m ² . Alternatively, the total surface area (unit: m ² ) of the conductive material contained in the electrode for a lithium secondary battery may be expressed as a value divided by the total weight (unit: g) of the active material.

Since the electrode for a lithium secondary battery according to the present invention includes a conductive material having a surface area of 0.01 to 3.5 m ² , specifically 0.5 to 3 m ² per 1 g of the active material, a side reaction with the electrolyte can be reduced And excellent high-temperature storage performance can be exhibited.

In one example of the present invention, the conductive material may surround the surface of the active material. At this time, since the conductive material includes both the linear conductive material and the point conductive material, it is possible to reduce the blocking of the pores of the surface of the cathode active material.

The surface area of the conductive material surrounding the surface of the active material per 1 g of the active material surrounding the surface of the conductive material may be 0.01 to 3 m ² , and may be specifically 1.0 to 2.9 m ² .

In the present invention, the surface area can be measured by a BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured by the BET 6-point method by a nitrogen gas adsorption / distribution method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. The conductive material may be graphite such as natural graphite or artificial graphite, acetylene black, ketjen black, channel black, Carbon black such as black and thermal black; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive metal oxides such as titanium oxide; And conductive materials such as polyphenylene derivatives. Specific examples thereof include graphite such as natural graphite and artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black And the like.

The linear conductive material may be conductive fibers such as carbon fibers, carbon nanofibers (CNF), and metal fibers; Conductive tubes such as carbon nanotubes (CNT); Conductive whiskers such as zinc oxide and potassium titanate, and specifically may be at least one selected from the group consisting of carbon nanofibers, carbon nanotubes, and mixtures thereof.

The linear conductive material may have an aspect ratio of 1:10 to 1: 80,000 and may have an aspect ratio of 1:20 to 1: 60,000, more specifically, 1:40 to 50,000. When the aspect ratio is less than 10, there is a problem that the battery conductivity is poor. When the aspect ratio is more than 80,000, there is a problem that the dispersibility of the linear conductive material is deteriorated.

The linear conductive material may have a length of 0.1 to 200 탆, specifically 0.5 to 50 탆, and more specifically 1 to 5 탆. The width (diameter of the cross section perpendicular to the longitudinal direction) may be 5 to 80 nm, specifically 8 to 12 nm. . When the length of the linear conductive material is in the range of 0.1 to 200 탆, the effect of using the linear conductive material as described above, which is distinguished from the point conductive material, can be exerted.

The linear conductive material may be specifically carbon nanotubes. More specifically, the linear conductive material may be a bundle-type carbon nanotube having an average strand diameter of 15 nm or less of the carbon nanotube unit.

Since the carbon nanotubes have a very high strength and a high resistance to fracture, it is possible to prevent repetition of charging and discharging and deformation of the current collector due to external force. In addition, oxidation of the surface of the current collector in an abnormal battery environment such as high temperature and overcharge can be prevented, so that the safety of the battery can be greatly improved.

The carbon nanotube is a secondary structure of the carbon nanotubes per unit formed are set to fulfill the bundled in whole or in part, the CNT units has a cylindrical form of the graphite surface (graphite sheet) The nano-sized diameter, sp ² Bonding structure. At this time, depending on the angle and structure of the graphite surface, the characteristics of the conductor or semiconductor may be exhibited. The carbon nanotube unit can be classified into a single walled carbon nanotube (SWCNT), a double walled carbon nanotube (DWCNT), a multiwall carbon nanotube (MWCNT), a multi- walled carbon nanotube), and the thinner the wall thickness, the lower the resistance. The carbon nanotube may be a single-walled carbon nanotube, a multi-walled carbon nanotube, or a mixture thereof, and a functional group including a carboxyl group, a hydroxyl group, or both may be formed on the surface. The functional group may be formed by treating the carbon nanotubes with an acid, wherein the acid may be a strong acid such as nitric acid.

Typically, the carbon nanotubes (CNTs) may have different physical properties depending on the crystallinity, structure, shape, structure and shape of secondary particles composed of the unit, impurities, and components contained in the CNTs of the CNTs have. Accordingly, by controlling any one or two or more of the above factors in combination, it is possible to have the properties required according to the use of the linear transformer.

If the diameter of the carbon nanotube unit is too large as the conductive material for the secondary battery, the number of absolute strands per volume decreases, and the amount of the conductive material used increases. Therefore, the production of electrodes with high energy density is disadvantageous, The electrode density may be lowered. In addition, if the diameter of the carbon nanotube unit is too small, dispersion is difficult and the process for preparing the dispersion is poor, and the dispersed carbon nanotube unit or the carbon nanotube is buried in the space between the electrode active material particles, and sufficient pores are difficult to be formed. Accordingly, in an embodiment of the present invention, the average strand diameter of the carbon nanotube unit in the carbon nanotubes usable as the linear conductive material may be 15 nm or less, and the dispersibility of the conductive material in accordance with the diameter control of the unit may be improved, The average strand diameter of the carbon nanotube unit may be from 1 nm to 15 nm, more specifically from 3 nm to 12 nm, more preferably from 3 nm to 12 nm, nm.

As the length of the carbon nanotube unit is longer, the electrical conductivity, strength, and lifetime characteristics at room temperature and high temperature of the electrode can be improved. If the length of the carbon nanotube unit is short, it is difficult to form the conductive path efficiently, and there is a fear that the electric conductivity is lowered. On the other hand, if the length of the carbon nanotube unit is excessively long, there is a fear that the dispersibility is lowered. Accordingly, the length of the unit body in the carbon nanotubes usable in the present invention may be 0.5 to 200 탆. Also, considering the diameter of the carbon nanotube unit, the carbon nanotube unit has a length (a length of a long axis passing through the center of the unit) and a diameter (a length of the carbon nanotube unit passing through the center of the unit, The length of the minor axis) may be 10 to 80,000, more specifically 20 to 50,000.

In the present invention, the strand diameter and the length of the carbon nanotube unit can be measured using a field emission scanning electron microscope.

In the conductive material dispersion according to the embodiment of the present invention, the average diameter of the CNTs is small as described above, and the CNTs exhibit a high BET specific surface area and excellent dispersibility due to their large aspect ratio.

The BET specific surface area of the linear conductor used in the present invention may be 200 m ² / g to 330 m ² / g, more specifically 240 m ² / g to 280 m ² / g.

In the present invention, the specific surface area of the linear conductive material is measured by the BET method. Specifically, the specific surface area can be calculated from the amount of nitrogen gas adsorbed at a liquid nitrogen temperature (77K) using BEL Japan's BELSORP-mino II .

Also, in one embodiment of the present invention, the CNT that can be used as the linear conductive material has a maximum peak intensity (IG) of G band at 1580 ± 50 cm ^-1 obtained by Raman spectroscopy using a laser having a wavelength of 532 nm, The average value of the ratio (I _D / I _G ) of the maximum peak intensity ( _{D D} ) of the D band at 1360 ± 50 cm ^-1 to the peak intensity I _D / I _G of 0.7 to 1.7 and the standard deviation value of 1.3 to 2.0%.

Raman spectroscopy is a useful method for analyzing the structure of CNTs and for analyzing the surface state of CNTs. The peak in the region of the wavenumber of 1580 cm ^-1 in the Raman spectrum of CNT is referred to as a G band, which is a peak indicating the sp ² bond of the CNT, indicating a carbon crystal having no structural defect. On the other hand, the peak present in the region near the wavenumber 1360 cm ^-1 in the Raman spectrum is referred to as D band, and this is a peak indicating the sp ³ bond of CNT. When the atomic bond composed of sp ² bonds is broken to become an sp ³ bond, do. Since the D band increases when disorder or defect existing in the CNT is generated, the ratio of the maximum peak intensity I _D of the D band to the maximum peak intensity I G of the G band (I _D / I _G ) can be calculated to quantitatively evaluate the degree of disorder or defect generation.

In the present invention, the G band of Raman spectrum for CNT may be a peak present in a wavenumber range of 1580 ± 50 cm ^-1 , and the D band may be a peak present in a wavenumber range of 1360 ± 50 cm ^-1 . The wave number range for the G band and D band corresponds to a range that can be shifted according to the laser light source used in the Raman analysis method. The Raman value used in the present invention is not particularly limited, but can be measured at a laser wavelength of 532 nm using a DXR Raman Microscope (Thermo Electron Scientific Instruments LLC).

The larger the ratio between the G-band peak integration value and the D-band peak integration value, the larger the amount of amorphous carbon is contained or the crystallinity of CNT is poor. In the present invention, however, the BET specific surface area increases and the second The CNT has a good crystallinity and an average value and a standard deviation value of I _D / I _G as described above.

Also, in one embodiment of the present invention, the CNTs that can be used as the linear conductive material may be formed by doping a metal element derived from a main catalyst or a cocatalyst such as Co, Mo, V, or Cr used as an impurity . Specifically, the CNT may include metal elements Fe, Ni and Mo in a total amount of 3 mg / kg or less, more specifically 2 mg / kg or less, among the catalyst-derived metal elements, and more specifically, And may not contain at least any one of the above-described metal elements, that is, Fe, Ni and Mo, particularly Fe. As described above, by remarkably reducing the content of the metal elements, particularly the Fe metal, as impurities remaining in the carbon nanotube, it is possible to exhibit better conductivity without worrying about side reactions in the electrode.

The content of the residual metal impurities in the CNTs can be analyzed using inductively coupled plasma (ICP).

The CNT may be commercially available and used, or it may be used directly. For example, it may be manufactured by a conventional method such as an arc discharge method, a laser evaporation method, or a chemical vapor deposition method, and the physical properties described above may be realized through control of the kind of the catalyst, the heat treatment temperature, .

Specifically, when the carbon nanotubes are produced according to the chemical vapor synthesis method, the carbon nanotubes are prepared by contacting a supported catalyst carrying a metal catalyst on a spherical a-alumina support with a carbon source under heating to prepare carbon nanotubes, And selectively removing metallic impurities in the carbon nanotubes.

More specifically, the supported catalyst is introduced into a horizontal fixed bed reactor or a fluidized bed reactor, and the carbon nanotube according to the chemical vapor phase synthesis method is heated at a temperature not lower than the pyrolysis temperature of the gaseous carbon source or not higher than the melting point of the supported metal catalyst Carbon source; Or by injecting a mixed gas of the carbon source and a reducing gas (for example, hydrogen) and a carrier gas (for example, nitrogen) to decompose the carbon source to grow carbon nanotubes by a chemical vapor phase synthesis method . The carbon nanotubes produced by the chemical vapor synthesis method have a crystal growth direction nearly parallel to the tube axis and a high crystallinity of the graphite structure in the tube length direction. As a result, the diameter of the unit is small, and the electrical conductivity and strength are high.

Specifically, the carbon nanotubes can be produced at a temperature of 500 ° C or more and less than 800 ° C, more specifically, 550 ° C to 700 ° C. In the reaction temperature range, the weight of the carbon nanotubes is maintained while maintaining the bulk size of the carbon nanotubes while minimizing the generation of amorphous carbon, so that the dispersibility according to the reduction of the bulk density can be further improved. As the heat source for the heat treatment, induction heating, radiation heat, laser, IR, microwave, plasma, surface plasmon heating and the like can be used.

The carbon source can supply carbon, and can be used without limitation, as long as it can exist in a gaseous phase at a temperature of 300 ° C or higher. Specific examples of the carbon source include carbon monoxide, methane, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, Hexane, cyclohexane, benzene or toluene, and any one or a mixture of two or more of them may be used.

After the carbon nanotubes are grown by the heat treatment as described above, a cooling process for more regularly arranging the carbon nanotubes can be selectively performed. Specifically, the cooling process may be performed using a natural cooling or cooling device according to the removal of the heat source.

On the other hand, the supported catalyst used in the production of the conductive material is one in which a metal catalyst is supported on a spherical a-alumina support. The? -Alumina has a very low porosity as compared with? -Alumina and is very low in utility as a catalyst support. However, by controlling the firing temperature at which the supported catalyst is formed, it is possible to increase the diameter by reducing the specific surface area while suppressing the generation of amorphous carbon during the synthesis of carbon nanotubes. At the same time, the bulk density of the carbon nanotubes can be reduced to improve dispersibility.

The α-alumina usable as the support may have an average particle diameter (D ₅₀ ) of 20 to 200 μm and a BET specific surface area of 1 to 50 m ² / g. The? -Alumina may have a surface with a very low porosity, specifically, a porosity of 0.001 to 0.1 cm ³ / g.

On the other hand, the supported catalyst containing the spherical a-alumina as a support can be produced by carrying a metal catalyst on the spherical a-alumina support followed by firing. Specifically, the supported catalyst is prepared by adding the spherical a-alumina support to a metal catalyst precursor solution prepared by dissolving the precursor of the metal catalyst in water, and then mixing the mixture at a temperature of 600 ° C or lower .

The metal catalyst supported on the support functions to help the carbon components present in the gaseous carbon source to bond together to form a 6-membered ring structure. As the metal catalyst, a main catalyst such as iron, nickel or cobalt may be used alone, or the main catalyst may be used in the form of a main catalyst-cocatalyst complex catalyst together with a promoter such as molybdenum, vanadium or chromium . Specifically, the composite catalyst may be FeCO, CoMo, CoV, FeCoMo, FeMoV, FeV or FeCoMoV, and any one or a mixture of two or more of them may be used. The cocatalyst may be used in an amount of 0.01 to 1 mole, more specifically 0.05 to 0.5 mole, per mole of the main catalyst.

As the precursor of the metal catalyst that can be used in the preparation of the supported catalyst, a metal salt or metal oxide soluble in water may be used. Specifically, it may be a metal salt, a metal oxide or a metal halide including any one or two or more metal elements selected from among Fe, Ni, Co, Mo, V and Cr, Can be used. More specifically, the _{Co (NO 3) 2 · 6H} 2 O, Co 2 (CO) 8, [Co 2 (CO) 6 (t-BuC = CH)], Cu (OAc) 2, Ni (NO 3) 2 One or a mixture of two or more selected from the group consisting of 6H ₂ O, (NH ₄ ) ₆ Mo ₇ O ₂₄ .4H ₂ O, Mo (CO) ₆ , (NH ₄ ) MoS ₄ and NH ₄ VO ₃ is used .

The precursor of the metal catalyst may be used in the form of an aqueous solution dissolved in water, and the concentration of the metal catalyst precursor in the aqueous solution may be appropriately controlled in consideration of the impregnation efficiency and the like. Specifically, the concentration of the metal catalyst precursor in the aqueous solution may be 0.1 to 0.4 g / ml.

Also, the content of the spherical a-alumina support mixed with the metal catalyst precursor can be appropriately determined in consideration of the content of the support in the supported catalyst to be finally produced.

Acid can optionally be added to the metal catalyst precursor solution to control the bulk density of the carbon nanotubes. When an acid is further added, the metal catalyst precursor solution may be used in an amount corresponding to 3 to 40 mol, more specifically 5 to 30 mol, of the metal catalyst per mol of the acid. The acid may specifically be citric acid or the like, and any one or a mixture of two or more thereof may be used.

On the other hand, the mixing process of the metal catalyst precursor solution and the spherical a-alumina support may be carried out according to a conventional method, specifically, by rotating or stirring at a temperature of 45 ° C to 80 ° C .

In addition, the metal catalyst precursor and the support may be mixed in consideration of the content of the supported metal catalyst in the supported catalyst. As the amount of the metal catalyst supported on the supported catalyst increases, the bulk density of the carbon nanotubes produced using the supported catalyst tends to increase. Considering the bulk density of the carbon nanotubes thus produced, the metal catalyst may be mixed in an amount of 5 to 30% by weight based on the total weight of the supported catalyst.

After mixing the metal catalyst precursor solution and the spherical a-alumina support, a drying process may be optionally performed prior to the calcination process. The drying process may be carried out according to a conventional method, specifically, by rotary evaporation at a temperature of 40 ° C to 100 ° C under vacuum for 3 minutes to 1 hour.

Subsequently, firing is performed on the mixture of the metal catalyst precursor and the support prepared in the above-described manner. The firing may be carried out at a temperature of 600 DEG C or less, specifically 400 DEG C to 600 DEG C, in an air or an inert atmosphere.

After the drying step and before the firing step, a preliminary firing step may optionally be further performed at a temperature of 250 ° C to 400 ° C.

Considering the efficiency of the reaction, it is preferred that the α-alumina support is impregnated with at most 50% of the mixture of the metal catalyst precursor and the support immediately before the pre-baking, and the mixture of the remainder after the pre- Alumina support.

Meanwhile, in the CNT production method, the metal impurity removal step may be performed according to a conventional method such as washing and acid treatment.

The CNTs produced according to the above-described manufacturing method have a bundle shape, and since the CNT unit has a small strand diameter, excellent dispersibility and conductivity can be exhibited when the electrode is manufactured. In addition, it is possible to improve the conductivity in the electrode at a high purity, thereby improving the battery performance, especially the output characteristics of the battery at low temperatures, when the battery is applied.

On the other hand, the point conductive material and the linear conductive material may have a mixing ratio of 1: 0.1 to 1: 2 by weight, and more specifically, a mixing ratio of 1: 0.2 to 1: 1.

When the content of the linear conductive material to the conductive material is 1: 0.1 or more, an appropriate effect according to the addition of the linear conductive material can be exhibited. When the content of the linear conductive material to the conductive material is 1: 2 or less, The content of the linear conductive material becomes excessively large, and it is difficult to expect the effect of the addition of the point conductive material, and the problem of increased interface resistance and diffusion resistance of the battery can be prevented.

The conductive material may be 0.01 to 2 parts by weight, preferably 0.5 to 1.5 parts by weight based on 100 parts by weight of the active material. Since the electrode for a lithium secondary battery of the present invention includes both the point conductive material and the linear conductive material as the conductive material, it is possible to provide excellent electrical conductivity even with a small amount of conductive material as compared with the case where only the conductive material is used , The increase in the content of the conductive material reduces the adhesive force between the lithium metal oxide and the current collector, thereby making it difficult to achieve a desired performance.

Therefore, the amount of the conductive material included in the electrode for a lithium secondary battery of the present invention may be smaller than that of a conventional electrode for a lithium secondary battery, and the amount of the conductive material may be reduced so that the total surface area It is possible to solve the problem that the conductive material causes side reactions with the electrolytic solution, and the diffusion resistance can be reduced.

In one example of the present invention, the active material may have an average particle diameter (D ₅₀ ) of 0.1 to 30 μm, specifically 0.5 to 10 μm, more specifically, an average particle diameter of 1 to 5 μm.

In the present invention, the average particle diameter (D ₅₀ ) can be defined as a particle diameter based on 50% of the particle diameter distribution. The average particle diameter is not particularly limited, but can be measured using, for example, a laser diffraction method or a scanning electron microscope (SEM) photograph. In the laser diffraction method, it is generally possible to measure the particle diameter of about several millimeters from the submicron region, and high reproducibility and high degradability can be obtained.

The electrode for a lithium secondary battery according to an exemplary embodiment of the present invention may be a cathode or a cathode for a lithium secondary battery.

The electrode for a lithium secondary battery according to an exemplary embodiment of the present invention may be manufactured by a conventional method known in the art, for example, a method in which a slurry is prepared by mixing and stirring a solvent, a binder, a conductive material, And then dried. However, in order to maximize the effect of using the linear conductive material, the linear conductive material and the conductive material may be mixed in a different order of mixing. . Specifically, an electrode for a lithium secondary battery according to an exemplary embodiment of the present invention includes: (1) preparing a linear conductive material mixture including a binder and a linear conductive material; (2) adding an electrode active material to the linear conductive material mixture and mixing to prepare a mixture; And (3) preparing a slurry of an electrode active material by adding and mixing a mixture of the linear conductive material mixture and the electrode active material to a point conductive material.

(1) a step of producing a linear conductive material mixture comprising a binder and a linear conductive material

The step of preparing the linear conductive material mixture comprising the binder of the step (1) and the linear conductive material is preferably a step of dissolving the binder in a solvent to prepare a solution of the binder, and adding the linear conductive material A method of adding and mixing them; A method of dissolving and dispersing the binder and the linear conductive material in a solvent; And a method of preparing a solution in which the binder is dissolved in a solvent and a solution in which the linear conductive material is dispersed in a solvent, respectively, and mixing them.

The linear conductive material may be mixed with the solvent by a conventional mixing method such as a milling method such as a ball mill, a bead mill, a basket mill, For example, a mixing device such as a stirrer, a granulator, a bead mill, a ball mill, a basket mill, an impact mill, a universal stirrer, a clear mixer or a TK mixer.

At this time, in mixing the linear conductive material and the solvent, cavitation dispersion treatment may be performed in order to enhance the mixing property of the linear conductive material and the solvent or the dispersibility of the linear conductive material in the solvent. The cavitation dispersion treatment is a dispersion treatment method using a shock wave generated by rupture of vacuum bubbles formed in water when high energy is applied to a liquid, and can be dispersed without impairing the characteristics of the linear conductive material by the above method . Specifically, the cavitation dispersion treatment may be performed by ultrasonic wave, jet mill, or shear dispersion treatment.

The dispersion treatment process can be appropriately performed depending on the amount of the linear conductive material and the kind of the dispersant that may be additionally contained. Specifically, when performing the ultrasonic treatment, the frequency is in the range of 10 kHz to 150 kHz, the amplitude is in the range of 5 탆 to 100 탆, and the irradiation time can be 1 to 300 min.

As the ultrasonic wave generating apparatus for performing the ultrasonic wave processing process, for example, an ultrasonic homogenizer may be used. Further, when the jet mill treatment is performed, the pressure may be 20 MPa to 250 MPa, and may be performed a plurality of times, specifically, two or more times. As the jet mill dispersing apparatus, a high pressure wet jet mill or the like may be used.

The temperature during the cavitation dispersion treatment step is not particularly limited, but may be carried out at a temperature at which there is no fear of viscosity change of the dispersion due to evaporation of the solvent. Specifically, the temperature may be 50 ° C or lower, more specifically 15 ° C to 50 ° C Lt; / RTI > temperature.

The dispersant may be preferentially mixed with the linear conductive material, the binder, or both, and may be milled by a milling method such as a ball mill, a bead mill or a basket mill or a homogenizer, a bead mill, a ball mill, , A universal stirrer, a clear mixer, a TK mixer, or the like, and may be performed by a milling method using a bead mill.

In this case, the size of the bead mill may be suitably determined according to the kind and amount of the linear conductive material and the kind of the dispersant, and specifically, the diameter of the bead mill may be 0.5 mm to 2 mm.

When the electrode for a lithium secondary battery is a positive electrode for a lithium secondary battery, the binder may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, Polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, or Various types of binder polymers such as various copolymers can be used. As the solvent for forming the positive electrode, an organic solvent such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, dimethylacetamide Or water. These solvents may be used alone or in admixture of two or more. The amount of the solvent used is sufficient to dissolve and disperse the positive electrode active material, the binder and the conductive material in consideration of the coating thickness and the yield of the subsequent positive electrode slurry.

When the electrode for the lithium secondary battery is a negative electrode for a lithium secondary battery, the binder may be used to bind the negative electrode active material particles to hold the formed body. The binder is not particularly limited as long as it is a typical binder used for preparing the slurry for the negative electrode active material. (PTFE), polyvinylidene fluoride (PVdF), polyvinylidene fluoride (PVdF), polyvinylidene fluoride (PVdF), polyvinylidene fluoride (PVdF), polyvinylidene fluoride Polypropylene and the like may be used, and any one selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber and acrylic rubber, which are aqueous binders, or a mixture of two or more thereof may be used. The aqueous binders are economical, environmentally friendly, harmless to the health of workers, and are superior to non-aqueous binders, and have a better binding effect than non-aqueous binders. Thus, the ratio of the active materials of the same volume can be increased and the capacity of the aqueous binders can be increased. Preferably styrene-butadiene rubber can be used.

The binder may be contained in an amount of 10 wt% or less, specifically 0.1 wt% to 10 wt%, based on the total weight of the slurry for the negative electrode active material. If the content of the binder is less than 0.1 wt%, the effect of the binder is insufficient, which is undesirable. If the content of the binder is more than 10 wt%, the relative content of the active material may decrease to increase the binder content. not.

Examples of the solvent for forming the negative electrode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent to be used is sufficient to dissolve and disperse the negative electrode active material, the binder and the conductive material in consideration of the coating thickness of the slurry and the production yield.

(2) adding an electrode active material to the linear conductive material mixture and mixing to prepare a mixture

In step (2), an electrode active material is added to the linear conductive material mixture prepared in step (1) and mixed to prepare a mixture. In this step, the linear conductive material is placed on the surface of the active material.

(3) preparing a slurry of an electrode active material by adding a point conductive material to a mixture of the linear conductive material mixture and the electrode active material, and mixing

In step (3), a paste-like conductive material is added to the mixture of step (2) and mixed to prepare an electrode active material slurry.

A method of manufacturing an electrode for a lithium secondary battery according to an exemplary embodiment of the present invention is characterized in that the mixing order of the linear conductive material and the conductive material is different in the process of mixing the active material and the conductive material, Since the linear conductive material is positioned on the surface of the active material, the pore of the active material surface can be minimized.

The electrode active material slurry thus prepared may be coated (coated) on a current collector of a metal material, compressed and then dried to form an active material layer on the current collector to produce an electrode.

The active material layer formed by drying the active material slurry of the electrode for a lithium secondary battery may have a porosity of 10 to 40%, specifically, a porosity of 19 to 30%, more specifically 23 to 28%.

Since the active material layer of the electrode for a lithium secondary battery can have a porosity of 10% or more by mixing the linear conductive material and the point conductive material, it is possible to secure a sufficient space for the electrolyte to penetrate into the active material layer, And the point-like conductive material are contained in the above-mentioned contents, the active material layer has a porosity of 40% or less.

When the electrode is an anode, the current collector of the metal material is a metal having a high conductivity and is a metal that can easily adhere to the slurry of the cathode active material, and does not cause a chemical change in the battery in the voltage range of the battery. There is no particular limitation as long as it has conductivity. For example, the surface of stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel may be subjected to surface treatment with carbon, nickel, have. In addition, fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. The current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric, and may have a thickness of 3 to 500 μm.

The cathode active material is preferably a layered compound such as lithium cobalt oxide [Li _x CoO ₂ (0.5 <x <1.3)], lithium nickel oxide [Li _x NiO ₂ (0.5 <x <1.3)], compound; Lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ , or [Li _x MnO ₂ (0.5 <x <1.3)], such as Li _{1 + x} Mn _{2 - x} O ₄ where x is 0 to 0.33; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , or Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 to 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like.

Meanwhile, in the electrode for a secondary battery according to an embodiment of the present invention, when the electrode is an anode, the slurry of the cathode active material may include a dispersant to increase dispersibility of the conductive material. The dispersant may be used in steps (1), (3), or both.

The dispersant may be a nitrile rubber, more specifically, a partially or totally hydrogenated nitrile butadiene rubber. The hydrogenated nitrile-butadiene-based rubber comprises a conjugated diene-derived structural unit, a hydrogenated conjugated diene-derived structural unit and an?,? -Unsaturated nitrile derived structural unit, and the hydrogenated conjugated diene- By weight to 80% by weight. When this content is included, the miscibility with the solvent is increased to increase the dispersibility of the conductive material, particularly, the linear conductive material, and to increase the solid-like characteristics of the conductive material dispersion. As a result, The stability can be improved. More specifically, it may contain 40 wt% to 70 wt% of the hydrogenated conjugated diene-derived structural unit.

Further, in consideration of the improvement of the dispersibility of the conductive material and the compatibility with the solvent, the content of the?,? - unsaturated nitrile-derived structural unit in the partially hydrogenated nitrile-butadiene rubber is preferably from 10% by weight to 50 By weight, specifically from 20% by weight to 40% by weight. When the repeating unit containing an alpha, beta -unsaturated nitrile structure is contained in the above-described content range, the dispersibility of the conductive material can be increased, and even if the amount of the conductive material to be added is small, high conductivity can be imparted.

Considering the improvement in solid-like characteristics of the conductive material dispersion according to the control of the content of the repeating unit structure constituting the rubber and the coating stability improvement effect of the electrode-forming composition containing the same, the hydrogenated nitrile-butadiene- 10 to 50% by weight of a conjugated diene-derived structural unit; 20 to 80 wt% of hydrogenated conjugated diene-derived structural units; And 10% by weight to 50% by weight of an?,? - unsaturated nitrile-derived structural unit.

In the present invention, the content of the nitrile structure-containing repeating unit in the hydrogenated nitrile-butadiene rubber is the weight ratio of the structural unit derived from?,? - unsaturated nitrile to the entire rubber, and the content thereof is measured according to JIS K 6364 Is a median value of the quantity quantified by measuring the amount of nitrogen generated and converting the amount of bonds from the molecular weight of acrylonitrile according to the wheat oven method.

The hydrogenated nitrile-butadiene-based rubber can be prepared by copolymerizing an?,? - unsaturated nitrile, a conjugated diene, and optionally other copolymerizable tertiary monomers (termonomer) and then hydrogenating the C═C double bond in the copolymer. At this time, the polymerization reaction and the hydrogenation process can be carried out according to a conventional method.

Specific examples of the?,? - unsaturated nitrile that can be used in the production of the hydrogenated nitrile-butadiene rubber include acrylonitrile and methacrylonitrile, and one kind or a mixture of two or more kinds of them may be used .

Specific examples of the conjugated diene which can be used in the production of the hydrogenated nitrile-butadiene rubber include conjugated dienes having 4 to 6 carbon atoms such as 1,3-butadiene, isoprene and 2,3-methylbutadiene, Or a mixture of two or more thereof may be used.

Examples of other copolymerizable tertiary monomers that can be optionally used include aromatic vinyl monomers such as styrene,? -Methylstyrene, vinylpyridine, and fluoroethyl vinyl ether),?,? -Unsaturated carboxylic acids (such as acrylic acid Unsaturated carboxylic acids such as methyl (meth) acrylate, ethyl (meth) acrylate, n-dodecyl (meth) acrylate, (Meth) acrylate, hydroxyethyl (meth) acrylate, or polyethylene glycol (meth) acrylate), anhydrides of?,? - unsaturated dicarboxylic acids (such as maleic anhydride, Citric anhydride, citraconic anhydride, etc.), but are not limited thereto.

In the hydrogenated nitrile-butadiene rubber produced according to the above-mentioned method, the structural units derived from the?,? - unsaturated nitrile, the structural unit derived from the conjugated diene, the structural unit derived from the hydrogenated conjugated diene and the structure derived from the other copolymerizable tertiary monomer The content ratio of the units may vary within a wide range, and in each case, the total sum of the structural units is 100% by weight.

The hydrogenated acrylonitrile-butadiene rubber (H-NBR) may have a weight average molecular weight of 10,000 g / mol to 700,000 g / mol, more specifically 10,000 g / mol to 300,000 g / mol. The partially hydrogenated acrylonitrile-butadiene rubber (H-NBR) has a polydispersity index PDI (Mw / Mn ratio, Mw is weight average molecular weight and Mn is number average Molecular weight). When the H-NBR has the weight average molecular weight and the polydispersity index within the above range, the carbon nanotubes can be uniformly dispersed in the solvent. In the present invention, the weight average molecular weight and the number average molecular weight are molecular weight in terms of polystyrene which is analyzed by gel permeation chromatography (GPC).

The dispersing agent may be included in an amount of 1 part by weight to 50 parts by weight based on 100 parts by weight of the conductive material. When the content of the dispersing agent is less than 1 part by weight, it is difficult to uniformly disperse the conductive material in the dispersion. When the amount exceeds 50 parts by weight, viscosity of the dispersion may increase. More specifically 10 to 25 parts by weight.

When the electrode is a cathode, the current collector of the metallic material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples thereof include copper, gold, stainless steel, aluminum, nickel, titanium, , Surfaces of copper or stainless steel surface treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric. The current collector of the metal material may have a thickness of 3 to 500 mu m.

As the negative electrode active material used for the negative electrode, a carbon material capable of occluding and releasing lithium ions, lithium metal, silicon or tin may be used. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high-temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The negative electrode may further include a thickening agent for adjusting the viscosity as needed.

The thickening agent may be a cellulose compound, and may be at least one selected from the group consisting of carboxymethylcellulose (CMC), hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, and specifically, carboxymethylcellulose (CMC), and the negative electrode active material and the binder may be dispersed in water together with the thickening agent to be applied to the negative electrode.

The present invention also provides a lithium secondary battery including the electrode for the lithium secondary battery. At this time, the electrode for the lithium secondary battery may be a cathode or an anode, specifically, a cathode. When the electrode for a lithium secondary battery is a positive electrode, the positive electrode may be manufactured according to the method for manufacturing an electrode for a lithium secondary battery according to an example of the present invention described above, and the negative electrode may be manufactured according to a conventional method known in the art .

Meanwhile, the lithium secondary battery may include a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-methacrylate copolymer The porous polymer film made of a polymer may be used alone or in a laminated form, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber, or the like may be used. no.

The lithium salt that can be used as the electrolyte used in the present invention may be any of those commonly used in electrolytes for lithium secondary batteries, and examples thereof include F ^- , Cl ^- , Br ^- , I ^- , NO _{3 ^{-, N (CN) 2 -}} , BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF ^{_{3) 5 PF -, (CF}} 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 ^{_{(CF 3) 2 CO -,}} (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^-, and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Examples of the electrolyte used in the present invention include an organic-based liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. no.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example 1: Preparation of positive electrode for lithium secondary battery

0.08% by weight of hydrogenated nitrile butadiene rubber (H-NBR) and 0.4% by weight of carbon nanotubes (CNT, specific surface area 250 m ² / g) as a linear conductive material were added to N-methyl-2-pyrrolidone And then ultrasonic wave of frequency 60 kHz was applied for 15 minutes using an ultrasonic homogenizer to prepare a dispersion of the linear conductive material.

0.1% by weight of hydrogenated nitrile butadiene rubber (H-NBR) and 1.0% by weight of carbon black as a spot-like conductive material were added to N-methyl-2-pyrrolidone (NMP) as a solvent. Using an ultrasonic homogenizer Ultrasonic waves at a frequency of 60 kHz were applied for 15 minutes to prepare a dispersion of the spot-like conductive material.

To the dispersion of the linear conductive material was added LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , and then the dispersion of the spot-type conductive material was mixed to prepare a cathode mixture slurry. The specific surface area of the conductive material was 2.32 m ² based on 1 g of the active material.

The prepared positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to prepare a positive electrode, followed by roll pressing to prepare a positive electrode.

Example 2: Preparation of positive electrode for lithium secondary battery

In the same manner as in Example 1 except that 2% by weight of carbon black and 0.2% by weight of H-NBR were used in the process of producing the dispersion of the spot-like conductive material in Example 1 To prepare a positive electrode.

Comparative Example 1: Preparation of positive electrode for lithium secondary battery

LiNi ₀ as cathode active material _{. 6} Co _{0 . 2} Mn _{0 .} 95% by weight of ₂ O ₂ , 3% by weight of carbon black as a conductive agent, 1.7% by weight of PVdF as a binder and 0.3% by weight of H-NBR were added to a solvent N-methyl-2-pyrrolidone (NMP) A mixture slurry was prepared. The specific surface area of the conductive material was 3.79 m ² based on 1 g of the active material.

The anode mixture slurry was coated on an aluminum (Al) thin film as a cathode current collector having a thickness of about 20 占 퐉 and dried to produce a cathode, followed by roll pressing.

Example  3: Preparation of lithium secondary battery

&Lt; Preparation of negative electrode &

1.5 wt% and 1.2 wt% of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders were mixed in a solvent NMP (96.3 wt%) as a negative electrode active material, To prepare a negative electrode active material slurry. The prepared slurry of the negative electrode active material was applied to a copper (Cu) thin film as a negative electrode current collector having a thickness of 10 mu m and dried to prepare a negative electrode, followed by roll pressing to prepare a negative electrode.

&Lt; Preparation of non-aqueous electrolytic solution &

LiPF ₆ was added to a nonaqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate as an electrolyte at a volume ratio of 30:70 to prepare a 1 M LiPF ₆ nonaqueous electrolyte solution.

&Lt; Production of lithium secondary battery >

After a positive electrode prepared in Example 1 and the positive electrode and the negative electrode prepared above were used to make a mixed separator of polyethylene and polypropylene therebetween, a cylindrical polymer type battery was produced by a conventional method, The prepared non-aqueous electrolyte solution was injected to complete the production of a lithium secondary battery.

Example 4: Preparation of lithium secondary battery

A lithium secondary battery was produced in the same manner as in Example 3, except that the positive electrode prepared in Example 2 was used as the positive electrode in Example 3 above.

Comparative Example 2: Production of lithium secondary battery

A lithium secondary battery was produced in the same manner as in Example 3 except that the positive electrode prepared in Comparative Example 1 was used as the positive electrode.

Experimental Example 1: Resistance Element Analysis

The resistive elements of the respective lithium secondary batteries prepared in Examples 3 and 4 and Comparative Example 2 were evaluated by using a pulse discharge profile and EIS measurement, and then, based on the resistance of the lithium secondary battery of Comparative Example 2, The increase / decrease is expressed in%. The results are shown in Table 1.

25 C, SOC 50 Example 3 Example 4 Comparative Example 2 Carbon black 1%
+ CNT 0.4% Carbon black 2%
+ CNT 0.4% Carbon black 3%
(standard) Conductive material Specific surface area
(m ₂ / active material g) 2.32 3.60 3.79 R _ohm + 2% + 12% - R _ct + 1% + 2% - R _diff -2% + 2% - R _sum - + 5% -

In Table 1, R _ohm represents the ohmic resistance, R _ct represents the charge transfer resistance, R _diff represents the diffusion resistance, and R _sum represents the total _sum of the resistances.

Referring to Table 1, the lithium secondary batteries of Examples 3 and 4 used a smaller amount of the conductive material than the lithium secondary battery of Comparative Example 2, but the increase in the resistance value was not large. Particularly, in Example 3, And the total amount of carbon nanotubes (CNTs) is 1.4%, the resistance value is comparable to that of Comparative Example 2 where 3% of carbon black is used. Also, since the use amount of carbon black, which is a point conductive material, can be reduced while using CNT, which is a linear conductive material, Compared with Comparative Example 2, the R _diff value can be reduced.

Experimental Example 2: Reference performance test

Each of the lithium secondary batteries prepared in Examples 3 and 4 and Comparative Example 2 was subjected to pulsed discharge (DC-IR measurement) by SOC section using a hybrid pulse power characterization (HPPC) method to record the resistance. The resistance was calculated by dividing the voltage change at discharge by the discharge current (R = V / I). The results are shown in Fig.

Experimental Example 3: Evaluation of high temperature storage stability

Each of the lithium secondary batteries prepared in Examples 3 and 4 and Comparative Example 2 was subjected to charging / discharging for 1 cycle at a current of 0.1 C, and initial discharge capacity and resistance were measured. The battery is then charged until it reaches 5 mV with a constant current (CC) of 0.1 C and then charged to a constant voltage (CV) until the charge current reaches 0.005 C (cut-off current) For 7 weeks, and then charged / discharged repeatedly at a current of 0.1 C every 1 week to measure the capacity retention rate and resistance of the battery. The results are shown in Fig.

In FIG. 2, the left axis represents the capacity recovery rate and the right represents the resistance value after high temperature storage (SOC50). The high temperature storage is performed in the full charge (SOC100), and after the high temperature storage, the monocell is recharged and discharged to obtain the capacity. At this time, the resistance (RPT) is measured again in the SOC.

Referring to FIG. 2, in the case of the lithium secondary battery of Example 3, the resistance and the capacity decrease were smaller than those of the lithium secondary battery of Comparative Example 2, and the deterioration of the output of the lithium secondary battery of Example 3 was smaller than that of Comparative Example 2 It can be seen that it is less than lithium secondary battery.

On the other hand, the lithium secondary battery of Example 3 exhibited excellent high temperature storage performance as compared with the lithium secondary battery of Comparative Example 2, and shows a low resistance increase rate. This is because the specific surface area of the conductive material contained in the anode is smaller than that of the lithium secondary battery of Comparative Example 2 in the case of the lithium secondary battery of Example 3 as shown in Table 1 above.

Experimental Example 4: Measurement of the resistance change when a high current is applied

The resistance of each lithium secondary battery manufactured in Example 3 and Comparative Example 2 was measured at 25 ° C for 30 seconds at 13.5 C based on SOC 50% (cut off voltage: 1.9 V). The resistance is expressed by the resistance method (ASI, area specific impedance) by multiplying the resistance by the area of the electrode, and the result is shown in FIG.

Referring to FIG. 3, the resistance of the lithium secondary battery of Example 3 is lower than that of the lithium secondary battery of Comparative Example 2 after 20 seconds. This is because the concentration polarization resistance is improved by improving the pore structure in the electrode It is estimated that the pore structure of the positive electrode active material is improved in the case of the positive electrode of Example 1 including the lithium secondary battery of Example 3. [

Claims (19)

An electrode for a lithium secondary battery comprising an active material and a conductive material,
Wherein the conductive material is a mixture of a point conductive material and a linear conductive material,
Wherein the conductive material has a surface area of 0.01 to 3.5 m ² per 1 g of the active material.
The method according to claim 1,
Wherein the conductive material surrounds the surface of the active material,
Wherein the surface area of the conductive material surrounding the surface of the active material per 1 g of the active material surrounding the surface of the conductive material is 0.01 to 3 m ² .
The method according to claim 1,
The point conductive material is at least one selected from the group consisting of graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, fluorocarbon, aluminum, nickel powder, conductive metal oxide, and polyphenylene derivatives Or more, an electrode for a lithium secondary battery.
The method according to claim 1,
Wherein the linear conductive material is at least one selected from the group consisting of carbon fibers, carbon nanofibers (CNF), metal fibers, carbon nanotubes (CNT), and conductive whiskers.
The method according to claim 1,
Wherein the linear conductive material comprises bundle-type carbon nanotubes having an average strand diameter of 15 nm or less of the carbon nanotube unit.
6. The method of claim 5,
Wherein the carbon nanotube has a specific surface area of 200 m ² / g to 330 m ² / g.
6. The method of claim 5,
The carbon nanotube has a maximum peak intensity of D band at 1360 +/- 50 cm &lt; ^-1 &gt; relative to the maximum peak intensity (I _G ) of G band at 1580 + 50 cm &lt; ^-1 &gt; obtained by Raman spectroscopy using a laser of 532 nm wavelength. Wherein an average value of the ratio (I _D / I _G ) of the electrode (I _D ) is 0.7 to 1.7 and a standard deviation value is 1.3 to 2.0%.
6. The method of claim 5,
Wherein the carbon nanotubes include metal elements including Fe, Ni, and Mo in a total amount of 3 mg / kg or less.
6. The method of claim 5,
Wherein the carbon nanotubes are produced using a catalyst that does not contain at least one metal element selected from the group consisting of Fe, Ni and Mo.
The method according to claim 1,
Wherein the linear conductive material has a length of 0.1 占 퐉 to 200 占 퐉.
The method according to claim 1,
Wherein the linear conductive material has a width of 5 nm to 80 nm.
The method according to claim 1,
Wherein the point conductive material and the linear conductive material have a mixing ratio of 1: 0.1 to 1: 2 by weight.
The method according to claim 1,
Wherein the conductive material is present in an amount of 0.01 to 2 parts by weight based on 100 parts by weight of the active material.
The method according to claim 1,
Wherein the active material has an average particle diameter (D ₅₀ ) of 0.1 to 30 μm.
The method according to claim 1,
Wherein the electrode for a lithium secondary battery includes an active material layer formed on a current collector,
And the porosity of the active material layer is 10% to 40%.
A lithium secondary battery comprising the electrode for a lithium secondary battery according to any one of claims 1 to 15.
17. The method of claim 16,
Wherein the electrode for the lithium secondary battery is a positive electrode.
17. The method of claim 16,
The lithium secondary battery is used in a medium to large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.
(1) preparing a linear conductive material mixture comprising a binder and a linear conductive material;
(2) adding an electrode active material to the linear conductive material mixture and mixing to prepare a mixture; And
(3) preparing a slurry of an electrode active material by adding and mixing a mixture of the linear conductive material mixture and the electrode active material, and forming a slurry of the electrode active material.

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